Memory Modules
| Two main types of industry-standard memory modules are used in laptops and portable computers today: SODIMM (small outline dual inline memory module) and MicroDIMM (micro dual inline memory module). There are four main types of SODIMMs and two main types of MicroDIMMs, with different sizes, speeds, and configurations available in each type (see Table 6.6). The SODIMM and MicroDIMM form factors and pinouts are JEDEC standards, which means that they are industry standards, thus ensuring conformity, compatibility, and interchangeability among different systems and manufacturers.
SODIMMs are mainly used by laptop or notebook computers, whereas the smaller MicroDIMMs are used mainly by subnotebooks, PDAs, and palmtop computers. SODIMMsMost laptop and notebook computers use SODIMMs (small outline dual inline memory modules), which are basically smaller and more compact modules than the standard DIMMs used in desktop systems. Although they differ in form factor and pinout, as compared to standard DIMMs, SODIMMs perform the same function. They allow for easy, modular memory installations and upgrades. The modules are inserted into sockets in the system and can easily be installed or removed. As the name implies, SODIMMs have different pins on each side of the module, with the odd-numbered pins on the front and the even-numbered pins on the back. Special keying notches on either side allow the module to be inserted into the connector only in the proper orientation. The notches are normally offset in their space for voltage keying as well. Various SODIMMs are available for different system requirements. Because they are not all interchangeable, you must be sure to match the correct type for a given system. 72-pin SODIMMThe 72-pin SODIMM is an older type used primarily in older 486 class portables. The 72-pin SODIMM reads and writes data 32 bits (4 bytes) at a time, which is a perfect match for 32-bit 486 processors. These modules are largely obsolete and are not used in any new system designs. They are still available for upgrading older systems, but because the supply is dwindling, the prices are higher than for newer, more modern modules. The 72-pin SODIMMs have the industry-standard form factor shown in the Figure 6.1. The 72-pin SODIMMs are available in several versions, with capacities of up to 64MB. Most utilize FPM/EDO memory chips, which are rated 60ns for speed and run on 3.3 volts. The most common sizes, including the depths and widths of the modules, are shown in Table 6.7.
The 72-pin modules have a 32-bit-wide data bus, which is equal to 4 bytes. For example, a 64MB 72-pin SODIMM is arranged internally as 16 million rows, with 32 bits (4 bytes) in each row, for a total of 64 million (16 million x 4) bytes. The JEDEC standard pinout for 72-pin SODIMMs is listed in Tables 6.8 and 6.9.
All SODIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. You should avoid modules with tin-plated contacts because tin will react with the gold plating on the connector contacts, causing corrosion and eventual memory failures. 144-pin SODIMMThe 144-pin SODIMMs are very popular in Pentium or Athlon class and newer laptop and notebook computers. They can read or write data 64 bits at a time, which makes them a perfect match for 64-bit processors such as the Pentium and newer chips. The 144-pin SODIMMs are available in several different memory chip types, including EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM versions. The 144-pin SODIMMs are not available in versions supporting error correcting code (ECC). When installing these modules, you must ensure that the type you are using matches the requirements of the system. In most cases, you can put a faster module in place of a slower one, but only if it is the same basic memory type. For example, you can usually install PC133 memory even if the system requires only PC100 or even 66MHz SDRAM, but you cannot use SDRAM modules in systems that require EDO, or vice versa. Also, you should not install modules that are slower than the system requires, even if they are the correct memory type. The speeds of 144-pin SODIMMs are rated as shown in Table 6.10.
The throughput or bandwidth is simply the frequency multiplied by the width, which gives the rate at which data can be read from or written to the module. Another specification to consider that is related to speed is the CAS (column address strobe) Latency, often abbreviated as CL. This is also sometimes called read latency, and it's the number of clock cycles occurring between the registration of the CAS signal and the resultant output data, with lower numbers of cycles indicating faster (better) performance. Typically, you find SDRAM modules rated CL 2 or CL 3. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the serial presence detect (SPD) ROM on the module and switch to slightly faster cycling rates. The 144-pin SODIMMs have the industry-standard form factor shown in Figure 6.2. All 144-pin SODIMMs have the odd-numbered pins (1143) on the front and even-numbered pins (2144) on the back and are 2.66" (67.6mm) long. The number of actual chips on the modules can vary, as can the physical height of the module. The modules are normally either 1" (25.4mm) or 1.25" (31.75mm) high, although the heights may vary slightly. The 144-pin SODIMMs use an SPD ROM (read-only memory) onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module and can be seen as component "U1" in Figure 6.2. The modules are keyed via a small notch in the connector area on the bottom (seen between pins 59 and 61 on the front), which prevents them from being installed backward and provides voltage keying as well. The voltage keying is shown Figure 6.3. Figure 6.3. 144-pin SODIMM voltage keying. Although the standard allowed for 5V modules, currently all 144-pin SODIMMs have the notch in the center position, indicating 3.3V operation. All the systems I am aware of will accept only 3.3V 144-pin modules, which draw less power and generate less heat. The 144-pin SODIMMs are available in several versions, with capacities of up to 512MB. They can utilize either EDO (extended data out) memory chips or SDRAM (synchronous dynamic RAM) at several different rated speeds. The most common sizes are shown in Table 6.11.
The capacity can be determined by multiplying the depth by the width. The 144-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 512MB 144-pin SODIMM is arranged internally as 64 million rows, with 64 bits (8 bytes) in each row, for a total of 512 million (64 million x 8) bytes. The JEDEC standard pinout for 144-pin SODIMMs using FPM or EDO RAM is listed in Tables 6.12 and 6.13.
The JEDEC standard pinout for 144-pin SODIMMs using SDRAM is listed in Tables 6.14 and 6.15.
All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. 200-pin SODIMMThe 200-pin SODIMMs are used to provide DDR (double data rate) and DDR2 SDRAM (synchronous dynamic RAM) memory for laptop computers. DDR2 SDRAM is the type of memory most recent high-performance laptops use. DDR modules run on 2.5 volts, whereas DDR2 modules use only 1.8V, making the DDR2 modules even more efficient for longer battery life. Each 200-pin SODIMM incorporates a 64-bit data path, which is ideal because these SODIMMs can be installed individually in 64-bit (Pentium and newer) systems. The 200-pin SODIMMs are available in PC1600 (200MHz), PC2100 (266MHz), PC2700 (333MHz), and PC3200 (400MHz) DDR SDRAM versions, as well as PC2-3200 (400MHz), PC2-4200 (533MHz), and PC2-5300 (667MHz) DDR2 versions. They are also available in versions supporting ECC (error correcting code), which offers 1-bit error detection and correction for greater integrity. Note, however, that ECC requires support from the chipset and motherboard, and very few laptops support this feature. When installing these modules, you must ensure the type you are using matches the requirements of the system. In most cases, you can put a faster module in place of a slower one, but only if it is the same basic memory type. Although both DDR and DDR2 modules have 200 pins and are the exact same size, they have slightly different pinouts and run on different voltages. To prevent installing the improper module type, the key notch is placed according to voltage. The notch is positioned to the left (facing the front of the module) for DDR modules (2.5V) and to the right for DDR2 modules (1.8V). The different notch positions make it impossible to fit the wrong module type into the socket. One thing the notch will not prevent, however, is installing a module that doesn't support the required speed. It is generally okay to install a module that is faster than the system requires, but you should not install a slower module than required by the motherboard. For example, you can usually install PC2700 memory even if the system requires only PC2100 or even PC1600, but if the system requires PC2700, you should not install the slower PC2100 or PC1600 modules. The speeds of 200-pin SODIMMs are rated as shown in Table 6.16.
The cycle time in nanoseconds (billionths of a second) matches the single data rate (SDR) clock speed, but double data rate (DDR) modules transfer twice per cycle, so the DDR frequency is always equal to double the SDR frequency. The throughput or bandwidth is simply the DDR frequency times the width, which gives the rate at which data can be read from or written to the module. Another specification to consider that is related to speed is the CAS (column address strobe) Latency, often abbreviated as CL. This is also sometimes called read latency, and it's the number of clock cycles occurring between the registration of the CAS signal and the resultant output data, with lower numbers of cycles indicating faster (better) performance. Typically, you can find DDR SDRAM modules rated CL 2 or CL 2.5. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD (serial presence detect) ROM on the module and switch to slightly faster cycling rates. The 200-pin SODIMMs have the JEDEC industry-standard form factor shown in Figures 6.4 (DDR) and 6.5 (DDR2). Figure 6.4. 200-pin DDR SDRAM SODIMM. Figure 6.5. 200-pin DDR2 SDRAM SODIMM. Note that the physical form factors for DDR and DDR2 are the same, except for the location of the key notch in the module. This prevents DDR modules from being installed in place of DDR2 modules and vice-versa. All 200-pin SODIMMs have the odd-numbered pins (1199) on the front and even-numbered pins (2200) on the back and are 2.66" (67.6mm) long. The number of actual chips on the module can vary, as can the physical height of the module. The modules are normally either 1" (25.4mm) or 1.25" (31.75mm) high, although some versions can be up to 1.5" (38.1mm) high (the heights may vary slightly). The taller modules may not fit in all systems, so be sure to check before ordering. Although the 200-pin modules are the same physical size as 144-pin modules, the pin spacing is tighter and the notch is offset much farther to the left, preventing the installation of 200-pin modules in 144-pin sockets, and vice versa. The 200-pin SODIMMs use an SPD ROM (read-only memory) onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module, much smaller than the memory chips, and may be mounted on the front or back side. The SPD chip can be seen as component "U9" in Figure 6.4. The modules are keyed via a small notch in the connector area on the bottom (seen between pins 39 and 41 on the front), which prevents them from being installed backward and provides voltage keying as well. The voltage keying is shown in Figure 6.6. Figure 6.6. 200-pin SODIMM DDR and DDR2 voltage keying. DDR modules are 2.5V, whereas DDR2 modules are 1.8V. The notch prevents plugging in modules of the improper voltage and type into a given system. The 200-pin SODIMMs are available in several versions, with capacities of up to 1GB. They utilize DDR or DDR2 SDRAM at several different rated speeds. The most common capacities are shown in Table 6.17.
The capacity can be determined by multiplying the depth by the width. The 200-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 1GB 200-pin SODIMM is arranged internally as 128 million rows, with 64 bits (8 bytes) in each row. If you multiply 128 million by 8, you get 1,024 million bytes, or 1GB. The JEDEC standard pinout for 200-pin SODIMMs is listed in Tables 6.18 and 6.19.
All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. Table 6.20 describes the pin functions.
MicroDIMMsMicroDIMMs (micro dual inline memory modules) are a newer and smaller type of memory module used mainly in subnotebooks, PDAs, and palmtop computers. As with all DIMMs, they have pins on both sides that perform different functions. The two main types of MicroDIMMs are 144-pin and 172-pin. The 144-pin versions contain SDRAM (synchronous dynamic RAM) and are similar to 144-pin SODIMMs, whereas the 172-pin versions contain DDR (double data rate) SDRAM and are similar to 200-pin SODIMMs. The MicroDIMMs are about half the size of the SODIMMs and yet offer similar capacities and performance. 144-pin SDRAM MicroDIMMThe 144-pin SDRAM MicroDIMMs are similar to the 144-pin SDRAM SODIMMs, but they're made to about half the physical size so as to fit the very tight form factors of smaller systems. Other than size, they have the same specifications as the 144-pin SDRAM SODIMMs, including the following features:
The 144-pin SDRAM MicroDIMMs are only 1.5" (38mm) long and 1.18" (30mm) high, which is about half the size of an equivalent SODIMM. Unlike SODIMMs, MicroDIMMs do not have any notches in the connector pin area; however, a notch is used on the left side to ensure proper insertion. They also have a unique size that is not interchangeable with other modules. The 144-pin SDRAM MicroDIMMs are available in PC100 and PC133 speeds. You can generally use PC133 modules in place of PC100 modules, but not the other way around. The speeds of 144-pin MicroDIMMs are rated as shown in Table 6.21.
The throughput or bandwidth is simply the frequency times the width, which gives the rate at which data can be read from or written to the module. As with SDRAM SODIMMs, another performance specification to consider that is related to speed is the CAS (column address strobe) Latency, often abbreviated as CL. Typically, you find SDRAM modules rated CL 2 or CL 3. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD ROM on the module and switch to slightly faster cycling rates. The 144-pin SDRAM MicroDIMMs have the industry-standard form factor shown in Figure 6.7. Figure 6.7. 144-pin SDRAM MicroDIMM. All 144-pin MicroDIMMs have the odd-numbered pins (1143) on the front and even-numbered pins (2144) on the back and are 1.5" (38mm) long and 1.18" (30mm) high. The number of actual chips on the modules can vary. The 144-pin MicroDIMMs use an SPD ROM onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module and can be seen as the smaller component "U5" in Figure 6.7. The modules are keyed via a small notch on the left side of the connector area, which prevents them from being installed backward. The 144-pin MicroDIMMs are available in several versions, with capacities of up to 256MB. The most common sizes are shown Table 6.22.
The capacity can be determined by multiplying the depth by the width. The 144-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 256MB MicroDIMM is arranged internally as 32 million rows, with 64 bits (8 bytes) in each row, for a total of 256 million (32 million x 8) bytes. The JEDEC standard pinout for 144-pin SDRAM MicroDIMMs is listed in Tables 6.23 and 6.24.
All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. 172-pin DDR SDRAM MicroDIMMThe 172-pin DDR SDRAM MicroDIMMs are similar to the 200-pin DDR SDRAM SODIMMs, but they're about half the physical size so as to fit the very tight form factors of smaller systems. Other than that, they have the same specifications as the 200-pin DDR SDRAM SODIMMs, including the following features:
The 172-pin DDR SDRAM MicroDIMMs are only 1.8" (45.5mm) long and 1.18" (30mm) high, which is about half the size of an equivalent SODIMM. Unlike SODIMMs, MicroDIMMs do not have any notches in the connector pin area; however, a notch is used on the left side to ensure proper insertion. They also have a unique size that is not interchangeable with other modules. Unlike the DDR SODIMMs, DDR MicroDIMMs do not support ECC (error correcting code) functions. The 144-pin SDRAM MicroDIMMs are available in PC1600, PC2100, and PC2700 speeds. You can generally use faster modules in place of slower modules, but not the other way around. The speeds of 172-pin DDR SDRAM MicroDIMMs are rated as shown in Table 6.25.
The cycle time in nanoseconds (billionths of a second) matches the single data rate (SDR) clock speed, but double data rate (DDR) modules transfer twice per cycle, so the DDR frequency is always double the SDR frequency. The throughput or bandwidth is simply the DDR frequency times the width, which gives the rate at which data can be read from or written to the module. As with DDR SDRAM SODIMMs, another performance specification to consider that is related to speed is the CAS (column address strobe) Latency, often abbreviated as CL. Typically, you find SDRAM modules rated CL 2 or CL 2.5. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD ROM on the module and switch to slightly faster cycling rates. The 172-pin SDRAM MicroDIMMs have the industry-standard form factor shown in Figure 6.8. Figure 6.8. 172-pin DDR SDRAM MicroDIMM. All 172-pin DDR SDRAM MicroDIMMs have the odd-numbered pins (1171) on the front and even-numbered pins (2172) on the back and are 1.8" (45.5mm) long and 1.18" (30mm) high. The number of actual chips on the modules can vary. The 172-pin DDR SDRAM MicroDIMMs use an SPD ROM onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module. The modules are keyed via a small notch on the left side of the connector area, which prevents them from being installed backward. The 172-pin DDR SDRAM MicroDIMMs are available in several versions, with capacities of up to 256MB. The most common sizes are shown in Table 6.26.
The capacity can be determined by multiplying the depth by the width. The 172-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 256MB MicroDIMM is arranged internally as 32 million rows, with 64 bits (8 bytes) in each row, for a total of 256 million (32 million x 8) bytes. The JEDEC standard pinout for 172-pin SDRAM MicroDIMMs is listed in Tables 6.27 and 6.28.
All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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