What is
parity ?
Memory parity was developed to
insure accurate system operation, it does not perform error
recovery, only error detection. When a memory parity error is
detected, usually the machine will halt or "lock up".
It was considered preferable for a machine to halt rather than
to run with corrupt data. With the highly reliable memory chips
produced today, parity checking is no longer required by most
systems. Parity requirement is a function of the system board.
On some newer system boards, this is a BIOS selectable option. 8
and 32 bit SIMMs have no parity. 9 and 36 bit have parity.
How do I
identify if my module has parity ?
This is easy on 30 pin SIMM's,
count the total number of chips on the SIMM board:
2 or 8 chips is non parity.
3 or 9 chips has parity.
72 pin modules are more
difficult, but generally if they have 4,8,16 or 32 chips on
them, they have no parity.
If you add a parity modules to a
non-parity system it will usually work . You can't however, add
non-parity modules to a motherboard designed for parity SIMMs.
How many
SIMMs are need ?
The following table gives the minimum
number of SIMMs required for different CPUs.
| Minimum
SIMM Requirements |
|
| CPU |
Data Width |
30 pin SIMMs Per Bank |
72 pin SIMMs per Bank |
| 386SX |
16 |
2 |
1 |
| 386DX |
32 |
4 |
1 |
| 486 |
32 |
4 |
1 |
| 586 |
64 |
8 |
2 |
| Pentiumtm |
64 |
8 |
2 |
| Power PC |
64 |
8 |
2 |
| PA-RISC |
64 |
n/a |
2 |
What is a
bank of memory ?
Computers will usually take
memory in 'banks'. Each bank carries the minimum number of SIMMs
required for the computer.
- A bank in a 486 machine would
consist of either four 30 pin SIMMs, or one 72
pin SIMM.
- A bank in a Pentiumtm
or PowerPCtm system is two
72 pin SIMMs.
- If a memory upgrade is
performed, SIMMs must be added to fill a bank. Banks are
normally labeled 0, 1, 2 etc.
- All SIMMs in each bank must be
of the same capacity.
Upgrading
memory on a PentiumTM.
The Pentium(tm) processor is a
true 64 bit data path processor. This design of the chip requires
that the 72 pin SIMMs be added in pairs. You cannot
use an odd number of 72 pin SIMMs with a Pentium(tm).
What is EDO
memory ?
EDO memory typically only works
on most newer Pentium motherboards.
It has the ability to read and write information 10-25% faster
than traditional fast page memory. EDO memory will only function
as EDO memory if it is used in a system with all EDO memory. If
mixed with standard memory it will sometimes work, but will act
like traditional fast page memory. There have been a few
problems reported when using EDO memory in conjunction with
Pipeline Burst Cache. This problem has been reported in only a
few system types.
It is best suited to processors
running at less than 166 MHz
What is
SDRAM
Synchronous Dynamic RAM uses the
processor's clock to synchronise its delivery of data, making it
the fastest DRAM currently available. Typical access speeds are
in the order of 6-10 nanoseconds. It is best suited to
processors running at 166 MHz and faster.
PC100 SDRAM for the BX and Apollo
Pro chipset has an access time of 7 - 8ns. Combined with the
increased bus speed users should expect a 10% performance
increase with this memory.
PC133 SDRAM for the 810e, 820, 840, Apollo Pro+ and KX133
chipsets has an access time of 6 - 7.5ns. Combined with the
increased bus speed users should expect a 10% performance
increase using this memory.
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