The Sundarban
Published Feb 19, 2026, 9:30 AM EST
Tony Phillips is an skilled Microsoft Express of commercial user with a twin-honors diploma in Linguistics and Hispanic Research. Prior to starting with How-to Geek in January 2024, he worked as a legend producer, knowledge supervisor, and affirm creator for over ten years, and loves making spreadsheets and documents in his spare time.
Tony will seemingly be an academic proofreader, skilled in reading, bettering, and formatting over 3 million words of non-public statements, resumes, reference letters, analysis proposals, and dissertations. Earlier than becoming a member of How-To Geek, Tony formatted and wrote documents for appropriate companies, including contracts, Wills, and Powers of Attorney.
Tony is obsessed on Microsoft Express of commercial! He’s going to gain any motive to create a spreadsheet, exploring ways to add complicated formulas and assume recent ways to make knowledge tick. He also takes pleasure in producing Observe documents that look the segment. He has worked as a knowledge supervisor in a secondary college in the UK and has years of expertise in the analysis room with Microsoft PowerPoint. He loves to bump into problems in Microsoft Express of commercial and use his expertise and appropriate-level coaching to gain alternatives.
Begin air of the Microsoft world, Tony is a alive to canine proprietor and lover, football fan, astrophotographer, gardener, and golfer.
In the event you are quiet saving Excel spreadsheets with a 3-letter .xls extension, you are lugging around a digital anchor from the expertise of dial-up. Previous being a Nineties relic, these legacy files are unimaginative, inclined to corruption, and—most dangerously—a most neatly-liked backdoor for unusual malware. It is time to trot to XLSX and by no formula look attend.
Cause 1: The binary shaded field vs. the unusual ZIP
To build why XLS needs to die, you’ve to look beneath the hood. In the unhurried Eighties, Microsoft equipped the Binary Interchange File Format (BIFF)—a proprietary format that only Excel certainly understands. These binary blobs are fragile: corruption in a single convey can render the entire workbook unreadable or extraordinarily complicated to restore.
In 2007, Microsoft bought excellent and switched to Express of commercial Begin XML (.xlsx), which is unquestionably staunch a renamed ZIP folder. Form no longer imagine me? Rename an XLSX file to .zip, and double-click it. It is seemingly you’ll per chance per chance gaze a highly organized directory of XML textual affirm files that deal with your knowledge, your cell kinds, and your workbook metadata individually.
Due to the XLSX file is modular, Excel can in total surgically restore a damaged workbook by changing one broken XML segment whereas keeping your raw knowledge.
Previous repairability, using XLS today limits gain admission to to unusual choices and can introduce performance inefficiencies in bigger or extra complicated workbooks. XLS quiet exists largely for backward compatibility, no longer as a consequence of it is technically superior.
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Cause 2: The safety minefield
In the event you need to make an IT supervisor recoil, staunch trace them a folder plump of XLS files. In the cybersecurity world, the ragged binary format is if truth be told a digital biohazard as a consequence of its opaque binary structure makes it harder for safety tools to look and isolate malicious code. This makes it a ideally suited “stealth” automobile for macro-primarily based totally mostly viruses and ransomware.
Customary XLSX files create no longer enhance macros by assemble. In the event you strive to save code in a single, Excel will warn you that the code will seemingly be stripped away unless you swap to a macro-enabled format (XLSM). What’s extra, Windows now makes use of Designate of the Web (MotW) to flag downloaded files with safety warnings. For legacy formats fancy XLS, this in total triggers safety warnings that many customers create no longer fully build.
Briefly, provocative to XLSX will get rid of the target from your attend. In an expertise where corporate electronic mail filters in total quarantine or block legacy attachments, using a most up-to-date format ensures your spreadsheets certainly attain your recipient’s inbox.
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Cause 3: The 65,536-row hump bump
In the Excel 97-2003 expertise, 65,536 rows and 256 columns seemed fancy an tons of quantity of information. On the other hand, in today’s expertise of extensive knowledge and automated experiences, it is no longer only a predominant limitation but also a knowledge-loss hazard.
The real hazard right here is unintended truncation. In the event you replica 100,000 rows of information into an ragged XLS workbook, Excel will warn you that knowledge previous the limit will seemingly be lost—but that warning is discreet to leave out at the same time as you are in a speed.
Recent XLSX workbooks, on the other hand, enhance 1,048,576 rows and 16,384 columns, and unusual choices, comparable to dynamic arrays and XLOOKUP, are built for this huge grid. Forcing them into an ragged binary format is fancy attempting to fit a V8 engine into a golf cart: finally, something will ruin.
Cause 4: Storage bloat and the 75% slim-down
If your hard drive is feeling the squeeze, that can even very neatly be as a consequence of the ragged XLS format is a storage hog. Due to these files store knowledge in a dense, uncompressed binary trot, they’re notoriously heavy. Provocative from XLS to XLSX is the digital identical of switching from an uncompressed suitcase to a vacuum-sealed fetch.
Since XLSX is a compressed ZIP kit, converting a legacy file can in total cut its dimension by 30% to 75% (looking on knowledge density and formatting) with out losing a single cell of information.
In addition to saving local disk convey, this makes each and each segment of your digital existence sooner. Smaller files imply quicker OneDrive syncing, sooner AutoSave performance, and fewer “attachment too large” bounces when emailing. In the event you are hoarding a entire bunch of ragged workbooks,
