Drobe :: The archives
About Drobe | Contact | RSS | Twitter | Tech docs | Downloads | BBC Micro

Confirm comment report request

The wear-levelling algorithms in ordinary consumer flash devices are nothing to do with FAT. Cheap consumer flash has a built-in wear-levelling algorithm, and it is normally formatted with FAT, but the two aren't related.

FAT is a ghastly filesystem used with DOS, nobody likes it but it became the de facto solution for devices which must be shared between a variety of machines simply because of the popularity of PCs running DOS.

The wear-levelling algorithms (except in high-end SSD devices) do something noddy like maintain some blocks in a ring buffer and rewrite the next available block in the ring on update. This avoids writing the same block over-and-over, and thereby extends the life of the device.

JFFS2 (and its predecessor JFFS and their successor LogFS) are intended for use with a software translation layer on raw flash devices ("memory technology devices") with no built-in wear levelling. So for example, a set top box with 2MB of RAM and 32MB of raw flash, might use JFFS2 to store some resources like graphics for its OSD. When you switch the box on, JFFS2 requires a full filesystem scan, but that's OK because 32MB doesn't take long and people leave their STBs in standby anyway.

FAT and JFFS2 are like car batteries and jet fuel, they may share some properties in theory, but they have no real applications in common.

 is a RISC OS Usertialaramex on 27/4/09 10:46AM
[ Reply | Permalink | Report ]

Click on the button below to confirm you wish to flag up this comment to the website's administrators. Abuse of this service will be frowned upon and it should only be used to notify us of comments that are extremely distasteful, indecent or otherwise unlawful. If you disagree with an opinion expressed or fact stated in a comment, please take part in the debate rather than expect it to be removed.

Return to the drobe.co.uk front page

Details

Reporting user / IP: / 54.80.137.168
Comment GID: 30583
Timestamp: Tue, 24 Oct 2017 03:56:24 +0000

Search the archives

Today's featured article

  • A9home: two years on
    We review the machine in its current state
     15 comments, latest by hzn on 7/1/08 10:50AM. Published: 4 Dec 2007

  • Random article

  • tofla moves to iconbar.com
    Coders' retreat expands
     6 comments, latest by krisa on 3/1/04 11:06PM. Published: 3 Jan 2004

  • Useful links

    News and media:
    IconbarMyRISCOSArcSiteRISCOScodeANSC.S.A.AnnounceArchiveQercusRiscWorldDrag'n'DropGAG-News

    Top developers:
    RISCOS LtdRISC OS OpenMW SoftwareR-CompAdvantage SixVirtualAcorn

    Dealers:
    CJE MicrosAPDLCastlea4X-AmpleLiquid SiliconWebmonster

    Usergroups:
    WROCCRONENKACCIRUGSASAUGROUGOLRONWUGMUGWAUGGAGRISCOS.be

    Useful:
    RISCOS.org.ukRISCOS.orgRISCOS.infoFilebaseChris Why's Acorn/RISC OS collectionNetSurf

    Non-RISC OS:
    The RegisterThe InquirerApple InsiderBBC NewsSky NewsGoogle Newsxkcddiodesign


    © 1999-2009 The Drobe Team. Some rights reserved, click here for more information
    Powered by MiniDrobeCMS, based on J4U | Statistics
    "..your knowledge seems to be below par"
    Page generated in 0.0505 seconds.