1 COMPUTER ARCHITECTURE (for Erasmus students) Assoc.Prof. Stasys Maciulevičius Computer Dept.

©S.Maciulevičius Standard interfaces Storage peripherals to PC computers can be connected using standard interfaces:  IDE (Integrated Drive Electronics) or ATA - one of the earliest and most significant standards introduced into PC hardware  EIDE (Enhanced IDE) - a standard designed to overcome the constraints of ATA while at the same time maintaining backward compatibility  SCSI - a much more advanced interface than IDE/ATA and has several advantages over IDE that make it preferable for many situations, usually in higher-end machines  SATA (Serial ATA) - a recent technological advancement of the standard IDE (ATA) hard drive interface

©S.Maciulevičius IDE The term Integrated Drive Electronics (IDE) refers not just to the connector and interface definition, but also to the fact that the drive controller is integrated into the drive, so drive can be connected directly to the system bus The IDE also known by another name - the ATA (AT Attachment) According to the specification the IDE can connect up to two drives, each with a capacity to 528MB (in 1986 it seemed that it would be sufficient)

©S.Maciulevičius IDE The ATA standard was originally intended for connecting hard drives, however an extension called ATAPI (ATA Packet Interface) was developed in order to be able to interface other storage peripherals (CD-ROM drives, DVD-ROM drives, etc.) on an ATA interface ATA cable has 3 connectors:

©S.Maciulevičius EIDE In 1994, about the same time that the ATA-1 standard was adopted, Western Digital introduced drives under a new name, Enhanced IDE (EIDE) These included most of the features of the forthcoming ATA-2 specification and several additional enhancements. Other manufacturers introduced their own variations of ATA-1 such as "Fast ATA" and "Fast ATA-2" EIDE greatly expanded the capacity limit - up to 8.4 GB, and later - up to 137 GB In drives disk caches were added

©S.Maciulevičius ATA standard The ATA standard is originally based on an asynchronous transfer mode, i.e. sending commands and sending data are clocked to the bandwidth of the bus and occur at each rising edge of the clock signal However, sending commands and sending data do not occur simultaneously, i.e. a command cannot be sent as long as the data has not been received and vice versa.

©S.Maciulevičius Ultra DMA  Ultra DMA was designed with the goal of optimising the ATA interface as much as possible  The first concept of Ultra DMA consists in using the rising edges as well as the falling edges of the signal for the data transfers, meaning an increase in speed of 100% (with the throughput increasing from 16.6 Mb/s to 33.3 Mb/s)  Moreover, Ultra DMA introduces the use of CRC codes for the detection of transmission errors

©S.Maciulevičius Ultra DMA modes Ultra DMA ModeThroughput (Mb/s) UDMA UDMA UDMA 2 (Ultra-ATA/33)33.3 UDMA UDMA 4 (Ultra-ATA/66)66.7 UDMA 5 (Ultra-ATA/100)100 UDMA 6 (Ultra-ATA/133)133

©S.Maciulevičius ATA Standards SpecificationIntroduce d Maximal bandwidth ATA-1 (IDE)19868 MB/s ATA-2 (EIDE) MB/s ATA MB/s ATA-4/ Ultra-ATA/ MB/s ATA-5/ Ultra-ATA/ MB/s ATA-6/ Ultra-DMA/ MB/s ATA-7/ Ultra-DMA/ MB/s

©S.Maciulevičius SATA With Parallel ATA (PATA) some problems were raised regard to cable length restrictions, the necessity of arbitration etc. In 2002 the first drives with the new interface – SATA – were produced Its speed – 150 MB/s and more. Its advantage - not just higher speed, but also thin cables (SATA cables have 7 wires, parallel ATA cables – 40 and even 80 wires !!!) These cables can reach a length of 1 m, while in parallel ATA - up to 40 cm

©S.Maciulevičius SATA (Serial ATA) Serial ATA is an enhancement to the ATA standard for for connecting storage to PC's All versions of ATA up until ATA-7 in 2004 utilized parallel transfer of data from the motherboard to the drive controller built onto the disk The ATA-7 specification introduced Serial ATA

©S.Maciulevičius SATA The original Serial ATA standard offered miniminal improvement over the existing 133MBps bandwidth of the existing Parallel ATA standard Serial ATA standards are constantly evolving to meet higher bandwidth requirements: SATA TypeBandwithBus SpeedSignal Rate SATA MBps1500MHz1.5Gbps SATA MBps3000MHz3.0Gbps SATA MBps6000MHz6.0Gbps

©S.Maciulevičius SATA Serial ATA utilizes a point-to-point architecture and improved design that offers these performance enhancements:  SATA removes the requirement for bus arbitration and, therefore, no I/O overhead is required for multiple device communication.  SATA has improved signal control and clocking as well as a hot-swap interface, which allows for higher frequencies with a lower risk of data loss.

©S.Maciulevičius SATA  SATA uses two differential signals on 4 signal pins that facilitate the isolation of data pins in the cable media. This will improve resistance to cross talk at higher frequencies  SATA offers error correction on interface and command data, greatly improving data integrity  SATA currently offers a maximum bandwidth of 150 MB/s* (*burst rate) for each drive. Since drives do not share the channel bandwidth with another drive, the overall performance of a multiple SATA drive solution will be measurably greater than that of a multiple ATA drive solution

©S.Maciulevičius eSATA Apart from the more common Universal Serial Bus (USB) and FireWire 400, another external interface used in data transfer is eSATA eSATA simply means External Serial Advanced Technology Attachment The main advantage of using eSATA is the fact that it is capable of transferring speed about three times faster than FireWire 400 and USB 2.0 eSATA allows the use of shielded cables up to 2 meters in length for external drives

©S.Maciulevičius SCSI standard  The SCSI standard (Small Computer System Interface) is an interface used to connect several different types of peripherals to a computer via a card, known as the SCSI adaptor or SCSI controller  The number of peripherals that can be connected depends on the width of the SCSI bus. With an 8- bit bus, 8 physical units can be connected and 16 for a 16-bit bus

©S.Maciulevičius SCSI

©S.Maciulevičius SCSI standards Standard Bus speed (MHz) Bus width Bandwidth, MB/s, Max SCSI Fast SCSI 108 Wide SCSI Fast Wide SCSI Ultra SCSI Ultra Wide SCSI

©S.Maciulevičius SCSI standards Standard Bus speed (MHz) Bus width Bandwidth, MB/s, Max Ultra-2 SCSI 408 Ultra-2 Wide SCSI Ultra3 SCSI (ULTRA- 160) Ultra-320 SCSI 80 DDR16320 Ultra-640 SCSI 80 QDR16640

©S.Maciulevičius SCSI vs SATA SATA is widely considered a product that will introduce new customers to RAID and expand the entry-level server market by reducing the cost of inexpensive redundant media. However, SATA has not been designed to replace SCSI SCSI has long been recognized as a high-end industrial server media technology in the area of performance There is a specification currently in design called Serial Attached SCSI (SAS). This will make improvements on the parallel SCSI interface and would be the logical replacement for SCSI

©S.Maciulevičius Serial Attached SCSI (SAS)  The SAS bus operates point-to-point. Each SAS device is connected by a dedicated link  SAS supports up to 16,384 devices through the use of expanders  SAS supports a higher transfer speed (3 or 6 Gbit/s) than most parallel SCSI standards  Both SAS and parallel SCSI use the SCSI command-set  Because of its higher signaling voltages, SAS can use cables up to 8 m long, SATA has a cable-length limit of 1 m  SAS controllers may support connecting to SATA devices, either directly connected using native SATA protocol or through SAS expanders