Improving transfer rates

[uweseimet]

There are several ways to improve transfer rates, depending on the bus and the drive or memory card. Various tools for measuring transfer rates are available. I recommend using XFERRATE. Values measured by different tools cannot be compared.
For SCSI and ACSI the maximum transfer rate is limited by the DMA hardware. The maximum for ACSI is about 1.3 MiB/s, for SCSI it is about 1.9 MiB/s. With IDE/SATA the transfer rate depends on the CPU and RAM speed and whether the hard disk driver runs in Fast-RAM or regular RAM. (HDDRIVER is the only driver that can be booted into Fast-RAM.) The highest known IDE transfer rate has been reached with a CTPCI board for the Falcon in 060 mode, with HDDRIVER in Fast-RAM and accelerated IDE mode enabled: 12.8 MiB/s. But also with a regular Falcon the IDE transfer rates are high, especially with the accelerated IDE mode.

Depending on the bus you can improve the transfer rate like this:

1. ACSI: With "Accelerated mode" in the "Performance" settings the ACSI bus timing is changed. Whether this leads to improvements depends on the drive and should be tested. Usually with fast ACSI peripherals the transfer rate increases.

2. IDE/SATA
a) The "Accelerated mode" switches in the "Performance" settings control the usage of the IDE READ/WRITE MULTIPLE IDE commands, which are supported by most hard drives. This mode can result in up to 25% higher transfer rates. Most memory cards usually do not support READ/WRITE MULTIPLE. This means that when transferring big chunks of data, the transfer rate of a memory card can be lower than with a hard drive. For smaller chunks of data the access time is often more relevant than the transfer rate and a memory card is faster.
b) Especially with an ST/STE the blitter is faster in transfering data than the CPU. Note that with the blitter option enabled, HDDRIVER makes use of the blitter regardless of the blitter settings in the GEM desktop.
c) Booting HDDRIVER into Fast-RAM is the fastest way of running a hard disk driver and in particular improves the IDE transfer rate. With a CTPCI board in 060 mode 12.8 MiB/s have been measuered, with a DFB1 wirh 50 MHz about 4.8 MiB/s HDDRIVER is the fastest driver for these platforms. HDDRIVER.SYS (and modules) can be installed in Fast-RAM by enabling the respective option in HDDRUTIL's "Basic Settings" before installing HDDRIVER. When HDDRIVER is loaded into TT-RAM on a TT, you cannot boot from ACSI but only from IDE or SCSI. Note that TT-RAM is not the same as Fast-RAM for a Falcon. TT-RAM supports SCSI/DMA, Fast-RAM for a Falcon does not. This results in reduced speed when transfering data from/to the Falcon's Fast-RAM via SCSI.
d) With a Raven Atari clone both types of RAM have identical speed. The transfer rate reported for the Raven is about 6.6 MiB/s, which makes HDDRIVER the fastest driver for the Raven.

3. ACSI, SCSI, IDE/SATA, USB
Using bigger GEMDOS caches results in a speed increase for file operations with any mass storage device. The bigger the caches, the less often a drive needs to be accessed. When running HDDRIVER in Fast-RAM, the caches are also located in Fast-RAM. This does not only save precious ST-RAM: Usually there is more Fast-RAM than ST-RAM, which means that the caches can be bigger. Maintaining very big GEMDOS caches incurs an overhead, though, i.e. very big caches may be counterproductive.
You can configure the GEMDOS cache sizes in HDDRUTIL's basic settings.

4. ACSI, SCSI
In case your Atari does not have any Alternate-RAM/Fast-RAM, you can increase the transfer rate for big blocks a little by selecting the respective option in the "Performance" settings. This will set the SCSI Driver's transfer size to the maximum size supported by the DMA hardware. By default the size is 64 KiB (the size of the _FRB buffer) for ACSI transfers with an ST or TT with Alternate-RAM, and for SCSI transfers with a Falcon that has Fast-RAM.

5. ACSI, SCSI
There is yet another way to improve the throughput: Background DMA with the MagiC operating system. The binaries for MagiCMac also contain MagiC for the Atari. With background DMA, which can be switched on in HDDRUTIL's "Basic Settings", ACSI and SCSI transfers run in the background without blocking active applications. This advantage adds to the general benefits offered by MagiC, like high speed and multitasking.