HP Kayak XU 04xx HP Kayak XU PC Workstation Technical Reference Manual Hardwar - Page 27

Devices on the Main Memory Bus, Main Memory

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2 System Board Devices on the Main Memory Bus Devices on the Main Memory Bus The memory bus is 72-bits wide, comprised of 64 bits of data and 8 bits of ECC. It is connected to the Main Memory and to the PAC (440LX) chip. Main Memory There are four 168-pin DIMM slots on the system board for installing main memory; slots A, B, C and D. All HP Kayak XU PC Workstation models are supplied with one memory module (either 32 MB, 64 MB or 128 MB ECC SDRAM) in one of the four DIMM slots, leaving three slots free for memory upgrades. Memory upgrades are available in single 32 MB, 64 MB or 128 MB memory modules. The maximum memory size of 512 MB is reached by using four 128 MB DIMMS. NOTE If ECC and non-ECC memory modules are both installed, ECC will be invalidated for all memory modules. Error Correcting Code Operation The error correcting code (ECC) memory of the HP Kayak XU PC Workstation allows any single bit error that occurs in any 72-bit line of memory (64 data bits plus 8 parity bits) to be corrected (automatically and transparently) by the PAC chip. A double bit error would cause an NMI to be generated, and the PC Workstation to be halted. If more bits are faulty within any given 72-bit line, the effect is the same as it would have been without error correction. The effect of executing a faulty instruction is always unpredictable, and might cause the program to 'hang'. The effect of reading a faulty data word is often similarly unpredictable, but can sometimes be tolerated (for instance, it might merely appear as a corrupted pixel on a video display). 19

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19
2
System Board
Devices on the Main Memory Bus
Devices on the Main Memory Bus
The memory bus is 72-bits wide, comprised of 64 bits of data and 8 bits of
ECC. It is connected to the Main Memory and to the PAC (440LX) chip.
Main Memory
There are four 168-pin DIMM slots on the system board for installing main
memory; slots A, B, C and D. All
HP Kayak XU PC Workstation
models are
supplied with one memory module (either 32 MB, 64 MB or 128 MB ECC
SDRAM) in one of the four DIMM slots, leaving three slots free for memory
upgrades. Memory upgrades are available in single 32 MB, 64 MB or 128 MB
memory modules. The maximum memory size of 512 MB is reached by using
four 128 MB DIMMS.
NOTE
If ECC and non-ECC memory modules are both installed, ECC will be
invalidated for all memory modules.
Error Correcting Code
Operation
The
error correcting code
(ECC) memory of the
HP Kayak XU PC
Workstation
allows any single bit error that occurs in any 72-bit line of
memory (64 data bits plus 8 parity bits) to be corrected (automatically and
transparently) by the PAC chip. A double bit error would cause an NMI to be
generated, and the PC Workstation to be halted.
If more bits are faulty within any given 72-bit line, the effect is the same as it
would have been without error correction. The effect of executing a faulty
instruction is always unpredictable, and might cause the program to ‘hang’.
The effect of reading a faulty data word is often similarly unpredictable, but
can sometimes be tolerated (for instance, it might merely appear as a
corrupted pixel on a video display).