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Advanced users

Serious tweaking of the CD-ROM cache

For CD_ROM dependent users As described previously, you can select a higher CD-ROM type than you actually have and thereby allocate a larger memory cache and read-ahead option.

If you are CD 'mad', have oodles of memory, and have a good quality CD drive, then you may benefit from the following - but note: it will not improve the performance of most games because they usually have their own in-built buffering


You are not restricted to the maximum settings presented by Windows in the CD-ROM options - CacheSize, and Read-ahead (Prefetch). Both of these can be increased further and will improved CD-ROM performance when used under Windows.

Note: The CD-ROM still performs only at its manufactured physical speed; however you can further increase those values to enhance your CD-ROM performance beyond the GUI limitations (depending on your CD-ROM physical speed, transfer rate and seek time).

These settings are in the Registry and can be altered with thpc_cd.reg files available from this Site (below).

A .reg files is installed by double-clicking it in Windows Explorer.
It installs immediately, without confirmation, and there is no Undo. Therefore caution is advised.

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Please note: It is generally accepted that a small CD-ROM cache makes a big difference in streaming performance, but a much larger cache does not pay off as significantly, unless the cache is large enough to contain entire multimedia streams.

A slight complication is that earlier versions of Windows 95 used the dword Registry setting; later versions use hex (hexadecimal) values. Therefore you must first look in your own Registry to see which type is used, and use the appropriate type.

Both types are included in the download. The hex versions have hx in the filename; dword versions have dw e.g. Cd16hx.reg for the hex version, or Cd16dw.reg for the dword version.

There are two changes to make (two .reg files to install) - one for the CacheSize and one for the Prefetch.

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Note 1: The defaults file CD_hx_DF.reg or CD_dw_DF.reg restores the Windows defaults for BOTH the CachSize and Prefetch. Use only the appropriate one if you wish to return to the default Windows CD-ROM settings (which is for a 4x CD-ROM with the Supplemental Cache Size set to Large).

Note 2: Two sizes are included for CacheSize:
medium (cshHXmed.reg or cshDWmed.reg) is the default x2
large (cshHXlrg.reg or cshDWlrg.reg) is the default x4
- note the different versions (hx and dw) in the filenames.

Note 3: Four sizes are included for the Prefetch
   the default multiplied by 2, x 4, x 6, and x 8

Note 4: Prior to use, you MUST FIRST READ the appropriate Read_1st.txt files that comes in the download

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To make a change you need to follow this procedure:

• Open your Registry with Regedit and follow the pathway -
  HKEY_LOCAL_MACHINE\System\CurrentControlSet \control\FileSystem\CDFS

• Identify (in the right pane) which value type is used
     6b 02 00 00 for a hex value type,
    0000026b for a dword value type

• Exit Regedit without making any changes

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• Open Windows Explorer to where you unzipped

CacheSize: Select the Hex or the DWord folder, then the CashSize folder. Now select either the Large or Medium cachesize reg file
Doubleclick will install it (without further confirmation)

Prefetch: Do likewise to get to the correct (hx or dw) Prefetch folder, and then select one of the files containing 8, 16, 24 or 32 (representing 8x, 16x, 24x or 32x)

• Restart Windows after a change

Uninstall: You can double-click on cd_hx_DF.reg or cd_dw_DF.reg (whichever is the correct value type for you) to restore the Windows defaults for BOTH the Prefetch and CachSize

You can experiment, selecting any combination of settings until you're satisfied with your CD-ROM performance.

Note: You need to restart Windows after the changes.

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Useful speed improvement will be seen for video clips, multimedia, and copying files.

Most games use their own in-built read-ahead and do not use the Windows prefetch, so a speed increase may not be obvious there.

All the above files are in the downloadable Zip file (12KB, freeware)

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As mentioned previously, you can compare your CD-ROM performance before, and again after, a change, and identify your optimal settings, by running a benchmark utility such as CDCheck (Windows 95/98, 124 KB, no nag shareware) or CD-Check (DOS, 12 KB, freeware)

A larger memory cache will only benefit those CD drives that can avail of a larger cache.

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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